Laser scanning microscope

ABSTRACT

An arrangement and corresponding method are provided for coupling radiation, preferably laser radiation, into a scanning head with a scanning unit in at least two dimensions. The radiation is focussed on an object via a microscope objective via at least one light-conducting fiber which is coupled with the scanning head. A collimator is arranged downstream of the fiber end at the scanning head for collimating the radiation exiting in a divergent manner at the fiber end.

This application claims benefit of provisional appln. 60/055,322 Aug.11, 1997.

BACKGROUND OF THE INVENTION

The present invention relates to a laser scanning microscope.

The following represents the prior art.

Handbook of Biological Confocal Microscopy, Second Edition, PlenumPress, New York and London 1995, page 519, FIG. 6: Fiber couplingoptics, page 595, FIG. 14: Telecentric system for a plurality ofdetection beam paths;

U.S. Pat. No. 5,283,433: Coupling optics for detection beam paths;

DE 4323129 A1, column 6: Confocal apertures which can be centered andvaried with respect to diameter;

U.S. Pat. No. 5,444,528, U.S. Pat. No. 5,377,003, U.S. Pat. No.5,317,379, U.S. Pat. No. 5,216,484: AOTF; U.S. Pat. No. 5,081,350, EP283256 A1, WO 90/00754: Fiber connection between laser and scanningunit.

OBJECT AND SUMMARY OF THE INVENTION

It is an object to provide an improved laser scanning microscope.

In accordance with the invention, an arrangement and correspondingmethod are provided for coupling radiation, preferably laser radiation,into a scanning head with a scanning unit in at least two dimensions.The radiation is focussed on an object via a microscope objective via atleast one light-conducting fiber which is coupled with the scanninghead. A collimator is arranged downstream of the fiber end at thescanning head for collimating the radiation exiting in a divergentmanner at the fiber end.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the present invention solely thereto, will best beappreciated in conjunction with the accompanying drawings, wherein likereference numerals denote like elements and parts, in which:

FIG. 1 shows a modular arrangement including microscope M, scanning headS, and laser unit;

FIG. 2 shows the beam path in the scanning head S;

FIG. 3 shows the optical effect of the displaceable collimating optics16;

FIG. 4 shows the optical effect of the pinholes which are displaceablein the direction of the optical axis;

FIG. 5 shows the optical effect of the pinholes which are displaceablevertically to the optical axis with different reflecting beam splitters;and

FIG. 6 shows the scanning head S, microscope M, and a fiber behind thepinhole in the detection beam path.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS List of ReferenceNumbers

M microscope

S scanning head

1 light source

2 illuminating optics

3 beam splitter

4 objective

5 specimen

6 condenser

7 light source

8 receiver

9 tube lens

10 tube lens

11 eyepiece

12 beam splitter

13.1, 13.2 lasers

14 light-conducting fibers

15 swivelable mirror

16 collimating optics

17 beam deflecting element

18 partially reflecting mirror

19 monitor diode

20 neutral filter

21 line filter

22 scanning objective

23 scanner

24 main beam splitter

25 imaging optics

26.1-26.4 detection channels

27 deflecting prism

28, 28.1, 28.2 dichroitic beam splitters

29 adjustable pinholes (pinhole diaphragm)

30 emission filter

31 PMT

32 AOTF

33 coupling-in optics

34 central driving unit

35, 36, 37, 38 local driving units for diode 19, filter changer 21,collimating optics 16, adjustable pinholes 29

39 beam splitter

40 light-conducting fiber

S1, S2, F1, F2 focus positions

P1, P2 pinhole positions

FIG. 1 shows schematically a microscope unit M and a scanning head Swhich share an optical interface via an intermediate imaging Z accordingto FIG. 2. The scanning head S can at the photo tube of an uprightmicroscope and also, in an advantageous manner, at a side output of aninverted microscope.

FIG. 1 shows a microscope beam path which is switchable betweenreflected-light scanning and transmitted-light scanning by means of aswivelable mirror 14, with light source 1, illuminating optics 2, beamsplitter 3, objective 4, specimen 5, condenser 5, light source 7,receiver arrangement 8, a first tube lens 9, an observation beam pathwith a second tube lens 10, and an eyepiece 11, as well as a beamsplitter for coupling in the scanning beam.

A laser module 13.1, 13.2 receives the lasers and is connected with thelaser coupling-in unit of the scanning head S via light-conductingfibers 14.1, 14.2. Coupling into the light-conducting fibers 14.1, 14.2is effected by means of displaceable collimating optics 16 which will bediscussed in more detail herein, and by means of beam deflectingelements 17.1, 17.2. A monitor beam path is reduced or stopped down inthe direction of a monitor diode 19 by means of a partially reflectingmirror 18; line filters 21 and neutral filters 20 are advantageouslyarranged in front of the monitor diode 19 on a rotatable filter wheel,not shown.

The actual scanning unit comprises a scanning objective 22, scanner 23,main beam splitter 24, and shared imaging optics 25 for detectionchannels 26.1 through 26.4. A deflecting prism 27 behind the imagingoptics 25 reflects the beam coming from the object 5 in the direction ofdichroitic beam splitter 28 in the convergent beam path of the imagingoptics 25, downstream of which are arranged pinholes 29, one for eachdetection channel, and emission filters 30 and suitable receiverelements 31 (PMT); the pinholes 29 are adjustable in the direction ofthe optical axis and vertically thereto and can be varied with respectto diameter.

As is shown schematically in FIG. 5, the beam splitters 27, 28 can beadvantageously constructed as a splitter wheel with a plurality ofpositions so as to be switchable by means of stepping motors.

UV radiation is advantageously coupled into glass fiber 14.1, preferablya single-mode glass fiber, by means of an AOTF as beam deflector, i.e.,when the beam should not fall on the fiber input, it is deflected fromthe fiber input, e.g., in the direction of a light trap, not shown, bythe AOTF.

The coupling-in optics 33 for coupling in the laser beam have lenssystems, not shown, for coupling in, the focal length of these lenssystems being determined by the beam cross section of the lasers and thenumerical aperture required for optimum coupling. Provided in the lasermodule 13.2 are single-wavelength and multiple-wavelength lasers whichare coupled into one or more fibers individually or jointly via an AOTF.

Further, coupling in can also be effected via a plurality of fiberssimultaneously, their radiation being mixed on the microscope side bycolor combiners after passing through adapting optics.

It is also possible to mix the radiation of different lasers at thefiber input; this mixing can be effected by means of the splitter mirror39, shown schematically, which is designed so as to be exchangeable andswitchable.

The laser beam emanating divergently from the end of the fibers 14.1,14.2 at the scanning unit S in FIGS. 2 and 3 is collimated to aninfinite beam by means of collimating optics 16. This is advantageouslyeffected by an individual lens which is displaced along the optical axisby means of a control unit 37 which is drivable by a central drive unit34 and therefore exercises a focussing function in that its distancefrom the end of the light-conducting fibers 14.1, 14.2 at the scanningunit can be varied by means of the invention.

The displacement effect of the collimating optics 16 is shownschematically in FIGS. 3a and 3b. FIG. 3a shows the beam configurationfor two different wavelengths λ1, λ2. Since imaging is effected for apolychromatic light source by stationary imaging optics in an imageplane only for a mean wavelength of the spectral region, the spacing ofthe fiber end and collimating optics is changed by the driving unit 37.Lens positions S1, S2 are given for the two shown wavelengths to ensurethe same focus position for both wavelengths. Accordingly, in the caseof fluorescence microscopy, the fluorescence radiation occurs in thefocus of the objective 4 which is adjusted to infinity and theexcitation radiation is focussed in the same plane.

Also, a plurality of fibers and fiber collimators can be used foradjusting different chromatic compensations for different excitationwavelengths. Further, a chromatic correction of the utilized optics,especially of the microscope objective, can be effected in this way.

Different chromatic compensations can be adjusted individually fordifferent wavelengths by means of a plurality of coupling-in fibers andcollimating optics. The variable collimation by means of displacement ofthe lens 16 can also be used to realize z-scanning in that the focus inthe specimen is displaced in the z direction by means of thedisplaceable collimator lens 16 and one optical section after the otheris detected. This is shown for a wavelength λ in FIG. 3b, wherein thefocus positions F1, F2 correspond to positions S1, S2.

In FIG. 2, a monitor diode 19 which can also have a focussing lens, notshown, placed in front of it acts in combination with a line-selectiveor region-selective filter wheel or filter slide 21, driven by a controlunit 36 for permanent monitoring of the laser beam coupled into thescanning module, especially to monitor in an isolated manner the outputin a determined laser line and, if need be, to stabilize it by means ofa regulating signal of the driving unit 34. The detection by means ofthe monitor diode 19 includes laser noise and variations due to themechanical-optical transmission system. In this respect, an error signalcan be derived from the detected instantaneous laser output, which errorsignal retroacts on-line directly on the laser or on an intensitymodulator (ASOM, AOTF, EOM, shutter) connected downstream of the laserfor the purpose of stabilizing the laser output radiated into thescanning module. A stabilization of intensity with respect to wavelengthand a monitoring of laser output can accordingly be effected bycontrolling the filter unit 21.

By means of a connection to the detection means 31 (PMT) and to thecentral driving unit, a noise reduction can be effected by taking thesignal quotient of and/or by signal subtraction of the detection signaland of the monitor signal of the diode 19 in that the correspondingsensor signal of a detection channel is normalized or standardized(e.g., division) with respect to the signal of the monitor diode bypixel as pixel-frame information in order in this way to reduceintensity fluctuations in the image.

FIG. 1, in a schematic view, shows pinholes 29 in the detection channels26.1-26.4, which pinholes 29 are adjustable in different ways. Inparticular, they can be arranged so as to be displaceable vertically tothe optical axis or in the direction of the optical axis and, in a knownmanner, so as to be variable in diameter, e.g., by means of a shearingmechanism or cat's eye. The adjustment of the pinhole diameter allowsthem to be adapted to the diameter of the Airy disk at differentobservation wavelengths.

FIGS. 4 and 5 show schematic views of driving means 38 for theadjustment or displacement of the individual pinholes which have datalines to the central driving unit 34. The controllable displacement ofthe pinhole in the direction of the optical axis is shown schematicallyin FIG. 4. It is advantageous for compensation of optical errors,especially chromatic longitudinal aberrations. These errors can occur inthe scanning objective 22, but also, for example, in the shared imagingoptics 25 for the detection channels.

Due to chromatic longitudinal deviations, different focus positionswhich correspond to different pinhole positions P1, P2 result fordifferent wavelengths λ1, λ2. When exchanging imaging optics, forexample, of the microscope objective, an automatic displacement of thepinhole can be effected along the optical axis via the driving unit 34and controlling and displacing means 38 with known chromaticlongitudinal aberrations of the utilized optics. An exact adjustment tothe utilized excitation wavelength can be carried out.

Due to the imaging optics 25 shared by all of the detection channels andadvantageously comprising only one optical element, the image atinfinity which is generated by the scanning objective 22 is imaged inthe pinhole plane. The shared imaging optic 25 brings about an improvedtransmission efficiency compared with known solutions. Nevertheless, anexact alignment can be effected in cooperation with the imaging opticswith individually adjustable. pinholes in the individual detectionchannels.

Different dichroitic beam splitters 28 can be used in the beam path,depending on the wavelength that is used, in order to block only thesewavelengths and direct them to a detection beam path. Therefore, thereare splitter turrets or splitter wheels (not shown) in different beampaths for swiveling in different splitters of the smallest possiblesize, especially splitter wheels whose wheel axis is inclined by 45°relative to the optical axis so that the splitters are always onlydisplaced in the reflection plane. Since the splitters 28 arranged onthe splitter wheels cannot be adjusted exactly alike and variations intheir alignment or standard wedge tolerances can cause different beamdeflecting angles, the respective pinhole is displaced via control unit38 vertically to the optical axis corresponding to the beam deflectionas is shown in FIG. 5. Shown here in a schematic view through differentpositions are two splitters 28.1, 28.2 on a splitter wheel, not shown,driven by a control unit 36, resulting in focus positions in the planeof the pinholes 29 displaced vertically to the optical axis. For thispurpose, a coupling of the position of the pinhole 29 with the splitterwheel position for the splitters 28 can be effected by means of thedriving unit 34 via the control units 36, 38, i.e., an optimum pinholeposition can be stored and called up for all splitter configurations ofdifferent splitter turrets. This applies not only for the position of adetermined splitter wheel, but also for the position of a plurality ofsplitter wheels, so that the respective optimum pinhole position isalways set automatically.

FIG. 6 shows schematically how a light-conducting fiber 40 can be placedat the pinhole 29 at the output to the PMT behind the pinhole in orderto guide the beam through the pinhole of the detection channel to anexternal sensor 31. This is advantageously effected without additionalcoupling optics close behind the pinhole by means of thelight-conducting fiber 38. Since the pinhole aperture is adjustable, theexchange of fibers with different core diameters is greatly simplifiedin that the pinhole size is adapted to the core diameter.

While the present invention has been particularly shown and described inconjunction with preferred embodiments thereof it will be readilyappreciated by those of ordinary skill in the art that various changesmay be made without departing from the spirit and scope of theinvention.

Therefore, it is intended that the appended claims be interpreted asincluding the embodiments described herein, the alternatives mentionedabove, and all equivalents thereto.

What is claimed is:
 1. An arrangement for coupling radiation, preferablylaser radiation, into a scanning head with a scanning unit scanning inat least two dimensions, comprising:a microscope objective for focussingthe radiation on an object; at least one light-conducting fiber coupledwith the scanning head, the radiation being focused on the object viasaid at least one light-conducting fiber; and a collimator arrangeddownstream of the fiber end at the scanning head for collimating theradiation exiting in a divergent manner at the fiber end.
 2. Thearrangement according to claim 1, wherein the collimator is displaceablein order to change its distance from the fiber end.
 3. The arrangementaccording to claim 2, wherein coupling in is effected via a plurality offibers for different wavelengths and/or wavelength ranges anddisplaceable collimators are arranged subsequent to each fiber output.4. A method for the operation of the arrangement according to claim 2,wherein an adjustment of the focus position is effected in a directionvertical to the two-dimensional deflection by means of the displacementof the collimating optics for a wavelength.
 5. A method for theoperation of the arrangement according to claim 2, wherein awavelength-dependent displacement of the collimating optics is effectedfor coupling in radiation of a plurality of wavelengths via a fiberand/or for different chromatic aberrations.